This invention relates to a method and an apparatus for liquid chromatography, and particularly to a method and an apparatus suitable for liquid chromatography where the flow rate of an eluting solution is low.
General principle of liquid chromatography is to fill an ion exchange resin or an adsorptive packing material into a separation column and feeding an eluting solution into the separation column, thereby separating components of an injected sample from one another. Examples of accurately measuring components to be detected by applying a special treatment to a sample are disclosed, for example, in Japanese- Patent Applications Kokai (Laid-open) Nos. 61-11662 and 55-132952.
With the higher speed of liquid chromatography, the feeding rate of an eluting solution has become smaller and consequently the volume of a separation column has become smaller. Thus, a volume of a sample to be introduced has also become smaller.
According to the conventional liquid chromatography, a predetermined, small amount of a sample is injected into the stream of the eluting solution and the components to be detected in the sample are separated from one another in the separation column. With the lower flow rate of the eluting solution by micro-liquid chromatography, the amount of a sample to be injected inevitably becomes a very trace amount and it is quite difficult to inject such a very trace amount of the sample into the eluting solution after the accurate volume measurement. For example, when the flow rate of an eluting solution is reduced to a few .mu.l/min., the amount of a sample will be in the order of nl, and it is practically difficult to accurately measure such a very trace amount of the sample.
On the other hand, the following prior art is disclosed in the field of ion chromatography, irrespectively of the reduction in the volume of a sample: Anal. Chem., 56 pp. 2073-2078 (1984), which suggests that anion species in an eluting solution are to be observed as absent peaks by continuously feeding only the eluting solution into a separation column and injecting distilled water into the stream of the eluting solution. However, the prior art suggests nothing of how to handle a liquid sample when the flow rate of the eluting solution is low.